The effects of Trimethyl aluminum (TMA) in atomic-layer-deposition (ALD) of La2O3 film using Tris(N, N'-diisopropylformamidinato) lanthanum and H2O were examined. The behaviors of Si diffusion and the residual C and N-related impurities were observed by in situ x-ray photoelectron spectroscopy. The La-silicate formation by Si out-diffusion from the substrate was suppressed by TMA/H2O pulse (Al2O3), but hardly suppressed the interfacial SiO2 layer growth during ALD. It was confirmed that TMA/H2O pulse (Al2O3) insertion eliminated the residual C-and N-related impurities with low binding energy in the La2O3 film which originated from the incomplete reactions of precursor during ALD. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3545965] All rights reserved.